This invention pertains to integrated resistors, and more particularly to vertically integrated resistors having an extremely high resistance.
It is well known in integrated circuit design and manufacturing that it is difficult to fabricate high value resistors on the order of 100 megohms or more. Conventional integrated resistors such as diffused resistors and thin film resistors do not generally have a high value of resistivity and are horizontally integrated with respect to the surface of the integrated circuit. Therefore, such conventional resistors require more die area than is practical for VLSI levels of integration.
The problem of fabricating high value resistors is especially noticeable in integrated memory arrays. A static RAM cell, for example, may contain two load resistors that each draw current from a power supply depending upon the cell state. Due to the large number of memory cells in the array, a low value load resistor causes excessive current flow into the chip, undesirably increasing power dissipation. For lower power dissipation and other factors such as high gain, it is highly desirable that each load resistor have a high resistance, on the order of 100 megohms or more. In certain applications, resistances on the order of a gigohm (10.sup.9 ohms) or even a terohm (10.sup.12) may even be required. However, such high value load resistances are not conventionally integratable into a memory array because of the excessive die area consumed.
Therefore, what is desired is a high value resistor that does not require excessive die area and can be practically fabricated in an integrated circuit process.